Mass transfer devices such as blood dialyzers commonly consist of a cylindrical cartridge containing a large number of thin hollow semipermeable membrane fibers extending generally longitudinally of the cartridge. The fibers are immersed in a bath of dialysate which is introduced into the cartridge in such a manner as to flow across the fibers, dialysis takes place through the surface of the fibers.
Normally, the dialysate used in blood dialysis is a saline solution of low viscosity. In accordance with recent research, however, better results have been obtained by the use of slurries which exhibit a much greater viscosity. Although the handling of both types of dialysates is generally similar, the physical structures best adapted to each type of dialysate differ.
The efficiency of the dialysis process depends to a substantial degree on producing flow patterns of the dialysate with respect to the fibers which avoid chaneling of the dialysate. In a conventional dialyzer, in which dialysate is simply introduced radially at one end of the cartridge and withdrawn radially at the other, there are a number of dead spots and areas of uneven flow distribution. Furthermore, a single generally axial pass of the dialysate through the cartridge does not give the dialysate enough contact time with the fibers to utilize its dialyzing capabilities to the fullest extent.